Photosensitive material



United States Patent Jersey No Drawing. Filed Feb. 7, 1958, Ser. No.713,807 14 Claims. (Cl. 96-92) This invention relates to brownprintpaper. Brownprint paper or Van Dyke paper as known in the art hasconventionally been produced by sensitizing a paper with a Watersolution of silver nitrate and a ferric salt.

It has been the practice in making engineering reproductions to use abrownprint as an intermediate negative. For example if it is desired tomake a duplicate of a tracing of an engir ieering drawing, a brownprintnegative is made from the tracing and a duplicate of the tracing is thenproduced on any suitable photosensitive material on a transparent base.The duplicate tracing can then be used for making additional blueprints,diazo types and the like. The negative brownprint material is usuallythough not always on so called transparent base material such astr-ansparentized paper, cloth, film or the like.

The usual brownprint material known in the art is generally made bycoating onto a high rag content paper, usually transparentized, asolution containing a watersoluble salt of silver, namely, silvernitrate, together with a complex ferric salt. The ferric salt may beeither a complex salt of an inorganic acid such as ferric ammoniumsulphate or a complex salt of an organic carboxylic acid. The organicacid may be a mono-, di-, or polycarboxylic acid, which advantageouslycontains one or more hydroxyl groups. For example ferric ammoniumcitrate and ferric ammonium oxalate have been used.

When brownprint material is exposed to light through a tracing or otheroriginal, the ferric salts are reduced to ferrous salts in the areasthat are struck by light. Subsequently, when the print is developed inthe presence of water, the ferrous salts in the light struck areasreduce the silver" salt in those areas to form the brown image. Theferrous salts that are formed by the action of light as well as theferric salts and silver salt in the unexposed areas are removed by thedeveloping solution. In order to help remove the exposed ferrous saltsan alkali salt of a polycarboxylic acid such as the sodium potassium orammonium salts of oxalic acid may be present in the developing solution.In order to prevent the formation of iron hydroxides the pH of thebrownprint sensitizing solution must be on the acid side. Preferablythis pH should be between 2 and 3. While certain of the complex ferricsalts used themselves exhibit an acid reaction, it may in other cases benecessary or advantageous in order to impart the acid reaction to thesensitizing solution to add free acid such as citric acid, tartaric acidor oxalic acid. After the development of a brownprint, it is customaryto fix the print with a solution of hypo to dissolve any remainingunexposed silver salts and then give it a final water wash to remove thefixing salts and any iron and silver salts dissolved thereby.

Prior art brownprint reproduction materials have several disadvantages.One of these is poor keeping quality of the light sensitive layer. It isbelieved that this is due to the fact that upon mixing and coating andduring storage nitrogen pentoxide is formed in this layer. This affectsnot only the photosensitive layer but may also contribute to thedestruction of the base material which may be an impregnated paper,cloth or the like. When brownprint sensitizing solutions are coated ontotracing cloth, it is customary to first waterproof the tracing cloth bymeans of a waterproof lacquer coating. The

3,038,803 Patented June 12, 1962 presence of nitrate in the brownprintsensitizing compo sition has a tendency to cause yellowing andbrittleness of this waterproof lacquer coating, which is anotherdisadvantage of the prior art brownprint sensitizers.

It has now been found that the above described disadvantages of theprior art brownprint materials may be overcome by substituting for thesilver nitrate commonly used, a silver salt which is ordinarilyconsidered insoluble in water. Silver salts such as silver carbonate,silver citrate and silver tartrate have been found to worksatisfactorily in the new brownprint sensitizing compositions. Generallyspeaking an improvement in the keeping quality of brownprint materialcan be achieved by replacing the silver nitrate with any silver salt ofa nonoxidizing inorganic or organic acid which has an ionizationconstant no more than that of another anion which appears in theformulation. Theoretically, in order to dissolve the silver salt, theionization constant of the acid of the anion which appears in the silversalt should be less than the ionization constant of the acid of anotheranion which appears in the formulation and this other anion should bepresent in at least equal stoichiometric proportions with the silversalt. It is believed that the fact that a silver salt of a nonoxidizingacid is used according to the present invention instead of the watersoluble silver salt, namely silver nitrate used in all prior artbrownprint processes accounts for a basic difference in the presentprocess and unexpected advantages over the prior art.

The following specific examples illustrate brownprint materials made upaccording to the present invention:

Example I Paper is coated in any known manner with the followingsolution:

Water cc 1000.0 Ferric ammonium citrate gm 127.0 Tartaric acid gm 21.0Silver carbonate gm 56.0

Days of Aginm O 5 10 15 20 Directions... 0 M O M C M O M G M Standard-AgNO; 331 320 10 58 3 22 2 8 1 1 Experimental Ag CO 346 396 102 121 10643 101 39 77 In the Schappers test the higher is the averaged figure,the greater is the resistance to tearing. The table clearly shows thatthe tendency of transparent brownprint paper to become brittle isreduced by the use of silver carbonate.

The success of the brownprint process depends also upon washing out thesolution from the unexposed areas. This process is slow and oftentimesincomplete so that there is discoloration in areas which should be thecolor of the base sheet. These discolorations result in poorreproductions when prints are subsequently made. Since silver carbonateor the other salts used according to this invention do not act upon thefibers of the paper, they do not adversely affect the keeping quality ofthe material and can be successfully washed off the unexposed areas '2at even on material which has been aged much longer than would bepossible with the prior art material.

Example 11 Fine quality tracing cloth Waterproofed by means of asuitable lacquer coating such as a nitrocellulose lacquer coating inknown manner is coated by any suitable known method with the followingsolution:

Ferric ammonium oxalate gm 90.0

Ferric oxalate gm 45.0 Tartaric acid. gm 25.0 Water cc 750.0 Polyvinylpyrrolidone 20% solution cc 175.0 Sodium hexametaphosphate solution cc50.0 Silver carbonate gm 45.0

This material is suitable for producing negative prints intended forrough handling or for the reproduction of maps. The sensitizing salts donot cause yellowing or embrittle the waterproof lacquer coating on thebackside of this waterproof tracing cloth. The coated material wassubjected to forced aging in a hot box at a temperature of 150 F. and55% relative humidity and there was no evidence of decomposition of thecoated layer or the base material.

Example 111 Fine quality tracing paper is coated in known manner withthe following solution:

Water cc 500 Ferric ammonium oxalate grams 30 Ferric oxalate c do 32Tartaric acid do 12 Silver citrate do 26 The ferric salts and tartaricacid are dissolved in water. Then the silver citrate is added in smallportions to the solution with constant stirring. When the reaction iscomplete, the solution is coated on the tracing paper base. Thesensitized material so prepared has very good shelflife.

Example IV Instead of the solution described in Example III, tracingpaper is coated with the following solution:

Water cc 150 Ferric ammonium oxalate grams 1 1 Ferric oxalate do 12.Oxalic acid do 5 Silver tartrate do 18 The sensitized material has thesame good properties described in Example III.

Having thus described the invention, what is claimed is:

1. A light sensitive material comprising a base sheet coated with alight sensitizing solution including a complex ferric salt containing inaddition to ferric ions at least one cation selected from the groupconsisting of NI-Lf Na+, and K+ and an anion selected from the groupconsisting of sulphate and organic carboxylates and a silver saltselected from the group consisting of silver carbonate, silver citrateand silver tartrate.

2. A light sensitive material comprising a base sheet coated with alight sensitizing solution including a complex ferric salt containing inaddition to ferric ions at least one cation selected from the groupconsisting of NH Na+, and K+ and an anion selected from the groupconsisting of anions of dicarboxylic acids and polycarboxylic acids anda silver salt selected from the group consisting of silver carbonate,silver citrate and silver tartrate.

3. A light sensitive material comprising a base sheet coated with alight sensitizing solution including a complex ferric salt containing inaddition to ferric ions at least one cation selected from the groupconsisting of NHJ, Na+, and K and an anion of a polycarboxylic acidcontaining at least one hydroxyl group and a silver salt selected fromthe group consisting of silver carbonate, silver citrate and silvertartrate.

4. A light sensitive material comprising a base sheet coated with alight sensitizing solution including ferric ammonium citrate and silvercarbonate.

5. A light sensitive material comprising a base sheet coated with alight sensitizing solution including ferric ammonium citrate and silvercitrate.

6. A light sensitive material comprising a base sheet coated with alight sensitizing solution including ferric sodium oxalate and silvercarbonate.

7. A light sensitive material comprising a base sheet coated with alight sensitizing solution including silver citrate, a complex ferricsalt containing in addition to ferric ions at least one cation selectedfrom the group consisting of NHJ, Na and K+ and an anion selected fromthe group consisting of citrate and oxalate.

8. A light sensitive material comprising a base sheet coated with alight sensitizing solution including silver tartrate, a complex ferricsalt containing in addition to ferric ions at least one cation selectedfrom the group consisting of NHJ, Na+ and K+ and an anion selected fromthe group consisting of citrate and oxalate.

9. A light sensitive material comprising a base sheet coated with alight sensitizing solution including a complex ferric salt containing inaddition to ferric ions at least one cation selected from the groupconsisting of citrate and oxalate, a silver salt selected from the groupconsisting of silver carbonate, silver citrate and silver tartrate and afree acid selected from the group consisting of citric acid, tartaricacid and oxalic acid.

10. A light sensitive material, comprising a base sheet coated with alight sensitizing solution including ferric ammonium citrate and silvercarbonate and being free from silver nitrate.

11. A light sensitive material, comprising a base sheet coated with alight sensitizing solution including ferric ammonium citrate and silvercitrate and being free from silver nitrate.

12. A light sensitive material, comprising a base sheet coated with alight sensitizing solution including ferric sodium oxalate and silvercarbonate and being free from silver nitrate.

13. A light sensitive material, comprising a base sheet coated with alight sensitizing solution including silver citrate and being free fromsilver nitrate, and a complex ferric salt containing in addition toferric ions at least one cation selected from the group consisting ofNHfi, Na+ and K+ and an anion selected from the group consisting ofcitrate and oxalate.

14. A light sensitive material, comprising a base sheet coated with alight sensitizing solution including silver tartrate and being free fromsilver nitrate, and a complex ferric salt containing in addition toferric ions at least one cation selected from the group consisting ofNI-Ifi, Na and K+ and an anion selected from the group consisting ofcitrate and oxalate.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Brown: Ferric and Heligraphic Processes, p. 41, 1900, Tennant& Ward, New York.

1. A LIGHT SENSITIVE SOLUTION INCLUDING A CONCOATED WITH A LIGHTSENSITIZING SOLUTION INCLUDING A COMPLEX FERRIC SALT CONTAINING INADDITION TO FERRIC IONS AT LEAST ONE CATION SELECTED FROM THE GROUPCONSISTING OF NH2+NA+, AND K+ AND AN ANION SELECTED FROM THE GROUPCONSISTING OF SULPHATE AND ORGANIC CARBOXYLATES AND A SILVER SALTSELECTED FROM THE GROUP CONSISTING OF SILVER CARBONATE, SILVER CITRATEAND SILVER TARTRATE.